The present invention relates generally to unloaders for portable containers and more specifically to an improved unloader suspension system and to an unloader specifically for side outlet portable containers.
Powdered, granulate or other particulate solid materials are transported, stored and dispensed in industrial processes from large portable containers or bins. The portable containers are delivered to a position where they are to be dispensed.
To aid the dispensing or discharge of the particulate material from the portable container, vibration means is generally provided. One type of prior art device has the portable container supported by a fixed frame upon which is mounted a dish-like material receiving means which is vibrated by a gyrator and which is isolated from the fixed frame by resilient compressional isolators. The dish-like receiving member and baffle which is received in the outlet of the portable container agitates and aids the dispensing of the particulate material. An example of this type of system is illustrated in U.S. Pat. No. 3,970,123. In another example of prior art, the portable bin is received by a vibrating frame which is interconnected to a fixed frame by compressional isolators. The vibration of the vibrational frame aids dispensing of the particulate material in the container. A typical example of the system is found in U.S. Pat. No. 3,854,612.
The compressional isolators by definition compress in response to the weight of the container and its contents. Since the weight of the container and its contents vary during dispensing, the height of the discharge nozzle may also vary. This variable displacement of the discharge nozzle from the container is undesirable in dispensing processes where a closely measured volume of material must be dispensed onto a moving belt or other flat conveyor using a fixed gate. The three sides of the nozzle and the belt in combination with the discharge gate determine the volume. The leading edge of the discharge gate causes a strike off. Thus the height of the nozzle will affect the volume per unit length of the belt, and consequently, any variation in height of the nozzle will affect this volume which must be controlled closely. It is obvious that compressional isolation systems for portable container unloaders will vary the height of the discharge nozzle with the weight of the material in the container or the discharge nozzle, thus is undesirable where the delivery volume must be accurate to be controlled. Another disadvantage of height variation of compression type isolators is when the unloader discharge nozzle is sealed (connected) to a downstream feeder in a dispensing process via a flexible sleeve. Variation in height of the nozzle can put undue strain on the seal causing it to slip from the surfaces on the unloader nozzle or downstream feeder to which it is clamped, thus ruining the dust-tight seal gained from use of the sleeve and causing material to leak out to the surroundings. Also, the response of compression-pression-type isolators vary with age and temperature and thus adds other uncontrollable factors. Since compressional isolators are dynamic and have moving parts, they have a limited useful life. The portable containers are generally placed and removed from the unloaders by fork lift trucks. Common pneumatic and liquid filled compressional isolators are susceptible to puncture from any inevitable bang of the fork of the lift trucks. Similarly, other dynamic compressional isolators may also be severely damaged. Thus, there exists a need for a static isolator system which is more rugged.
While the majority of the industry has directed its efforts to unloaders for bottom outlet portable containers, some efforts have been made to provide equivalent unloaders for side outlet portable containers. These efforts have been primarily directed to elevating a portion of the platform to an incline after the container is positioned upon the platform. These efforts have produced a device of unnecessary mechanical complexity which which results in increased costs and shortened useful life. Thus there exists a need for a more practical unloader for side outlet portable containers.